Present airbag/instrument panel coverstock technology uses PVC and/or PVC alloys for separate air bag doors and flip top instrument panel (IP) constructions. Recent airbag door design makes the door design integral to the coverstock. Upon deployment, the airbag breaks through the one piece IP coverstock. The coverstock materials and designs are therefore selected such that the deploying airbag pressure causes the coverstock to tear along a designed line.
When present technology PVC and PVC alloys are used on integral passenger side airbag doors, the deployed coverstocks tend to crack and fragment at cold temperatures. Coverstock fragmentation of the airbag door area creates air-borne debris that can cause personal injury to the passenger. Original equipment manufacturers have therefore promulgated testing requirements to identify and control this issue with respect to passenger vehicle systems. For example, reference is made to Chryslers' PF-9007 performance standard specification which addresses low temperature deployment considerations.
The deployment criteria of no fragmentation during deployment is also critical on both new as well as “end of life” vehicles. Along such lines, it is noted that a heat-aging test may be used to predict and understand the performance of an aged instrument panel. For example, it has been found that PVC and/or PVC alloys will sacrifice more than 35% of their original physical properties when exposed to temperatures equal to and above 110° C. for periods of 500 hours or longer. The tendency for PVC to become brittle after this kind of heat exposure causes excessive loss of physical properties, resulting in fragmentation of the material when deployed at cold temperatures.
The prior art has attempted to deal with modifying and adjusting plasticized PVC material as it relates to the development of a PVC alloy/blend formulation with improved low temperature performance characteristics. Along such lines attention is first directed to U.S. Pat. No. 3,006,889. The '889 patent relates to polymers of vinyl chloride and chlorinated polymers of vinyl chloride blended with chlorinated polyolefins. The '889 patent recites that it should especially be noted that an addition of a relatively large amount of chlorination products practically does not impair the good properties of polyvinyl chloride, but improves considerably the resistance to cold of polyvinyl chloride. The '889 patent goes on to say that it is desirable to increase resistance to the cold to avoid brittleness.
Attention is next directed to U.S. Pat. No. 5,525,284. The '284 patent relates to a thermoplastic microsphere for use in roto-casting or slush molding shells. The '284 patent discloses polyvinyl chloride material including pure PVC and alloys with PVC in the form of microspheres having a diameter of 0.007″ to 0.040″ suitable for roto-casting or slush molding.
Finally, attention is directed to U.S. Pat. No. 5,086,122, which recites chlorinated polyvinylchloride resins, which are crosslinked, to provide improved processing properties such as reduced processing torques. In addition, the '122 patent discloses blends of CPVC with non-crosslinked CPVC.
Accordingly, as can be seen from the above review, there exists a need for a material, suitable for use as the skin layer in an air bag deployment door, that will provide improved performance at low temperature, and which will also withstand the test of time and continue to provide good low temperature performance over the life of the vehicle.